The present invention relates to the use of GABAB receptor agonists for the inhibition of transient lower esophageal sphincter relaxations; for the treatment of gastro-esophageal reflux disease; and/or for the treatment of regurgitation in infants.
Reflux
In some humans, the lower esophageal sphincter (LES) is prone to relaxing more frequently than in other humans. As a consequence, fluid from the stomach can pass into the esophagus since the mechanical barrier is temporarily lost at such times, an event hereinafter referred to as xe2x80x9crefluxxe2x80x9d.
Gastro-esophageal reflux disease (GERD) is the most prevalent upper gastrointestinal tract disease. Current therapy has aimed at reducing gastric acid secretion, or by reducing esophageal acid exposure by enhancing esophageal clearance, lower esophageal sphincter tone and gastric emptying. The major mechanism behind reflux has been considered to depend on a hypotonic lower esophageal sphincter. However, recent research (e.g. Holloway and Dent (1990) Gastroenterol. Clin. N. Amer. 19, 517-535) has shown that most reflux episodes occur during transient lower esophageal sphincter relaxations (TLESR), i.e. relaxations not triggered by swallows. It has also been shown that gastric acid secretion usually is normal in patients with GERD.
Consequently, there is a need for compounds which reduce the incidence of TLESR and thereby prevent reflux. Ideally, the compound should have an effect duration of approximately 12 h, since most reflux occurs during daytime and postprandially.
A pharmaceutical composition comprising a local anaesthetic, adapted to inhibit relaxation of the lower esophageal sphincter, is disclosed in WO 87/04077 and in U.S. Pat. No. 5,036,057.
GABAB Receptor Agonists
GABA (4-aminobutanoic acid) is an endogenous neurotransmitter in the central and peripheral nervous systems. Receptors for GABA have traditionally been divided into GABAA and GABAB receptor subtypes. GABAB receptors (for a review see Kerr, D. I. B. and Ong, J. (1995) Pharmac. Ther. vol. 67, pp. 187-246) belong to the superfamily of G-protein coupled receptors. GABAB receptor agonists are described as being of use in the treatment of CNS disorders, such as muscle relaxation in spinal spasticity, cardiovascular disorders, asthma, gut motility disorders such as irritable bowel syndrome and as prokinetic and anti-tussive agents. GABAB receptor agonists have also been disclosed as useful in the treatment of emesis (WO 96/11680).
The GABAB receptor agonist baclofen (4-amino-3-(4-chlorophenyl)butanoic acid) (Swiss patent No. CH 449,046) has been the most studied of the GABA analogs. 
Other GABAB receptor agonists or partial agonists are disclosed in: EP 0356128; EP 0181833; EP 0399949; EP 0463969; and FR 2,722,192. For a review on the chemistry of GABAB modulators, see Froestl, W. and Mickel, S. J. in: The GABA Receptors, pp.271-296 (Eds. S. J. Enna and N. G. Bowery, Humana Press Inc., Totowa, N.J., U.S.A. 1997)
It is known in the art that drug screening can be improved by using cells which are transfected with a cloned receptor gene. Such transfected cells may offer several advantages over traditional screening, the most important being presumably selectivity. Another advantage of transfected cells is that they allow to assessment of the activity of drugs on cloned human receptors. The fact that the GABAB receptor has recently been cloned (Kaupmann et al., Nature 386(6622), 239-246, Mar. 20, 1997) thus offers the opportunity to to develop more specific drugs acting on the GABAB receptor. The said article discloses two subtypes of the receptor from rat, designated GABABR1a and GABABR1b, but it was made very clear that several other subtypes could be isolated.
It has been found surprisingly that GABAB receptor agonists can be used for the inhibition of transient lower esophageal sphincter relaxations, and thus for the treatment of gastro-esophageal reflux disease.
Consequently, the present invention provides the use of a GABAB receptor agonist for the manufacture of a medicament for the inhibition of transient lower esophageal sphincter relaxations (TLESR), or more specifically, for the treatment of gastroesophageal reflux disease. For the purpose of this invention, the term xe2x80x9cagonistxe2x80x9d should be understood as including both full agonists as well as partial agonists, wherby a xe2x80x9cpartial agonistxe2x80x9d should be understood as a compound capable of partially, but not fully, activating the GABAB receptor.
The inhibition of TLESR also implies that the compounds can be used for the treatment of regurgitation in infants. Effective managment of regurgitation in infants would be an important way of managing lung disease due to aspiration of regurgitated gastric contents, and for managing failure to thrive due to excessive loss of ingested nutrient.
In a preferred form of the invention, the GABAB receptor agonist is a substituted aminopropyl acid derivative where the acidic head is a carboxylic group, a phosphinic group, a phosphonous group or a sulfinic group.
Examples of compounds having agonistic or partially agonistic affinity to GABAB receptors and which thus can be used according to the invention are:
4-aminobutanoic acid (GABA),
4-amino-3-(4-chlorophenyl)butanoic acid(baclofen),
4-amino-3-phenylbutanoic acid,
4-amino-3-hydroxybutanoic acid,
4-amino-3-(4-chlorophenyl)-3-hydroxyphenylbutanoic acid,
4-amino-3-(thien-2-yl)butanoic acid,
4-amino-3-(5-chlorothien-2-yl)butanoic acid,
4-amino-3-(5-bromothien-2-yl)butanoic acid,
4-amino-3-(5-methylthien-2-yl)butanoic acid,
4-amino-3-(2-imidazolyl)butanoic acid,
4-guanidino-3-(4-chlorophenyl)butanoic acid,
3-amino-2-(4-chlorophenyl)-1-nitropropane,
(3-aminopropyl)phosphonous acid,
(4-aminobut-2-yl)phosphonous acid,
(3-amino-2-methylpropyl)phosphonous acid,
(3-aminobutyl)phosphonous acid,
(3-amino-2-(4-chlorophenyl)propyl)phosphonous acid,
(3-amino-2-(4-chlorophenyl)-2-hydroxypropyl)phosphonous acid,
(3-amino-2-(4-fluorophenyl)propyl)phosphonous acid,
(3-amino-2-phenylpropyl)phosphonous acid,
(3-amino-2-hydroxypropyl)phosphonous acid,
(E)-(3-aminopropen-1-yl)phosphonous acid,
(3-amino-2-cyclohexylpropyl)phosphonous acid,
(3-amino-2-benzylpropyl)phosphonous acid,
[3-amino-2-(4-methylphenyl)propyl]phosphonous acid,
[3-amino-2-(4-trifluoromethylphenyl)propyl]phosphonous acid,
[3-amino-2-(4-methoxyphenyl)propyl]phosphonous acid,
[3-amino-2-(4-chlorophenyl)-2-hydroxypropyl]phosphonous acid,
(3-amino propyl)methylphosphinic acid,
(3-amino-2-hydroxypropyl)methylphosphinic acid,
(3-aminopropyl)(difluoromethyl)phosphinic acid,
(4-aminobut-2-yl)methylphosphinic acid,
(3-amino-1-hydroxypropyl)methylphosphinic acid,
(3-amino-2-hydroxypropyl)(difluoromethyl)phosphinic acid,
(E)-(3-aminopropen-1-yl)methylphosphinic acid,
(3-amino-2-oxo-propyl)methyl phosphinic acid,
(3-aminopropyl)hydroxymethylphosphinic acid,
(5-aminopent-3-yl)methylphosphinic acid,
(4-amino-1,1,1-trifluorobut-2-yl)methylphosphinic acid,
(3-amino-2-(4-chlorophenyl)propyl)sulfinic acid,
3-aminopropylsulfinic acid.
Preferably, the compound having agonistic or partially agonistic affinity to a GABAB receptor is any one of the following compounds:
4-amino-3-(4-chlorophenyl)butanoic acid (baclofen),
(3-aminopropyl)methylphosphinic acid,
(3-amino-2-hydroxypropyl)methylphosphinic acid,
4-aminobutanoic acid (GABA),
(3-amino-2-(4-chlorophenyl)propyl)sulfinic acid,
(3-aminopropyl)(difluoromethyl)phosphinic acid,
(3-amino-2-oxo-propyl)methyl phosphinic acid,
4-amino-3-(5-chlorothien-2-yl)butanoic acid,
(3-aminopropyl)phosphonous acid.
The use of pharmaceutically acceptable salts of GABAB ligands for the disclosed purposes is also included in the invention. Most known GABAB ligands such as for example baclofen, (3-aminopropyl)methylphosphinic acid and (3-amino-2-(S)-hydroxypropyl)methylphosphinic acid are of amphoteric nature and may be present in the form of internal salts. They also can form acid addition salts and salts with bases. Such salts are particularly pharmaceutically acceptable acid addition salts, as well as pharmaceutically acceptable salts formed with bases. Suitable acids for the formation of such salts include, for example, mineral acids such as hydrochloric, hydrobromic, sulfuric or phosphoric acid or organic acids such as organic sulfonic acids and organic carboxylic acids. Salts of GABAB ligands with bases are, for example, alkali metal salts, e.g. sodium or potassium salts, or alkaline earth metal salts, e.g. calcium or magnesium salts as well as ammonium salts, such as those with ammonia or organic amines.
The use of optical isomers of GABAB ligands for the disclosed purposes is also included in the invention. Many known GABAB ligands such as for example baclofen and (3-amino-2-(S)-hydroxypropyl)methylphosphinic acid are chiral compounds due to the presence of an asymmetric carbon atom. Depending on the presence of asymmetric atoms, the GABAB ligands may be in the form of mixtures of isomers, particularly racemates, or in the form of pure isomers, especially enantiomers.
In another aspect, the invention provides a method for the inhibition of transient lower esophageal sphincter relaxations which comprises administration to a mammal, including man, in need of such treatment an effective amount of a GABAB receptor agonist as defined above.
Included in the invention is also a pharmaceutical composition for use in the inhibition of transient lower esophageal sphincter relaxations. More specifically, the pharmaceutical composition is useful for the treatment of gastroesophageal reflux disease and/or for treatment of regurgitation in infants. The active ingredient in the pharmaceutical composition can be any one of the GABAB receptor agonists as defined above.
Daily Dose
For use as an inhibitor of TLESR and as a reflux inhibitor, the GABAB receptor agonist may be used at doses appropriate for other conditions for which GABAB receptor agonists are known to be useful. The typical daily dose of the active substance varies within a wide range and will depend on various factors such as for example the individual requirement of each patient and the route of administration. In general, dosages will be in the range of 1 xcexcg to 100 mg per day and kg body weight, preferably 10 xcexcg to 10 mg per day and kg body weight.
Pharmaceutical Formulations
For clinical use, the compounds of the invention are formulated into pharmaceutical formulations for oral, rectal, parenteral or other mode of administration. The pharmaceutical formulation contains a compound of the invention in combination with one or more pharmaceutically acceptable ingredients. The carrier may be in the form of a solid, semi-solid or liquid diluent, or a capsule. These pharmaceutical preparations are a further object of the invention. Usually the amount of active compounds is between 0.1-95% by weight of the preparation, preferably between 0.2-20% by weight in preparations for parenteral use and preferably between 1 and 50% by weight in preparations for oral administration.
In the preparation of pharmaceutical formulations containing a compound of the present invention in the form of dosage units for oral administration the compound selected may be mixed with solid, powdered ingredients, such as lactose, saccharose, sorbitol, mannitol, starch, amylopectin, cellulose derivatives, gelatin, or another suitable ingredient, as well as with disintegrating agents and lubricating agents such as magnesium stearate, calcium stearate, sodium stearyl fumarate and polyethylene glycol waxes. The mixture is then processed into granules or pressed into tablets.
Soft gelatin capsules may be prepared with capsules containing a mixture of the active compound or compounds of the invention, vegetable oil, fat, or other suitable vehicle for soft gelatin capsules. Hard gelatine capsules may contain granules of the active compound. Hard gelatine capsules may also contain the active compound in combination with solid powdered ingredients such as lactose, saccharose, sorbitol, mannitol, potato starch, corn starch, amylopectin, cellulose derivatives or gelatin.
Dosage units for rectal administration may be prepared (i) in the form of suppositories which contain the active substance mixed with a neutral fat base; (ii) in the form of a gelatin rectal capsule which contains the active substance in a mixture with a vegetable oil, paraffin oil or other suitable vehicle for gelatin rectal capsules; (iii) in the form of a a ready-made micro enema; or (iv) in the form of a dry micro enema formulation to be reconstituted in a suitable solvent just prior to administration.
Liquid preparations for oral administration may be prepared in the form of syrups or suspensions, e.g. solutions or suspensions containing from 0.2% to 20% by weight of the active ingredient and the remainder consisting of sugar or sugar alcohols and a mixture of ethanol, water, glycerol, propylene glycol and polyethylene glycol. If desired, such liquid preparations may contain colouring agents, flavouring agents, saccharin and carboxymethyl cellulose or other thickening agents. Liquid preparations for oral administration may also be prepared in the form of a dry powder to be reconstituted with a suitable solvent prior to use.
Solutions for parenteral administration may be prepared as a solution of a compound of the invention in a pharmaceutically acceptable solvent, preferably in a concentration from 0.1% to 10% by weight. These solutions may also contain stabilizing ingredients and/or buffering ingredients and are dispensed into unit doses in the form of ampoules or vials. Solutions for parenteral administration may also be prepared as a dry preparation to be reconstituted with a suitable solvent extemporaneously before use.
Screening for Compounds Active Against TLESR
Further included in the invention is the use of cells, transfected with a nucleotide sequence encoding a GABAB receptor, for screening purposes, in order to identify inhibitors of transient lower esophageal sphincter relaxations. The GABAB receptor may be any one of the GABAB receptor subtype genes, such as GABABR1a or the GABABR1b or the hitherto uncloned subtypes of the GABAB receptor. The nucleotide sequences may be derived from any species, but preferably from a mammal and most preferably from man.
Consequently, the invention further provides a method for the screening of compounds which are inhibitors of transient lower esophageal sphincter relaxations, comprising the use of a nucleotide sequence encoding a GABAB receptor. In a preferred form such a method comprises the steps (a) transfecting a cultured cell with a nucleotide sequence encoding a GABAB receptor, so that a GABAB receptor is expressed on the surface of the cell; (b) contacting a test compound with the cell; and (c) determining whether the test compound binds to, and/or activates, the GABAB receptor. The GABAB receptor can e.g. be GABABR1a or GABABR1b.